Every modification to the Internl class affects all of its users, even when they should not be affected. For instance, when adding support to a new language, the users of the already-supported languages have to recompile (or worse: download) the new version. Moreover, as time goes by and support for new languages is added, the class becomes bigger, and its code harder to maintain. It takes longer to compile and contains more bugs. A bug introduced due to an addition of a new language will affect all users. Obviously, a much better choice is to use derivation: